c# 應用程式只運行一個執行個體

using System;
using System.Runtime.InteropServices;
using System.Windows.Forms;
using System.Diagnostics;
using System.Reflection;

namespace OneInstance
{
    /// <summary>
    /// Class with program entry point.
    /// </summary>
    internal sealed class Program
    {
        
        //Api聲明，並聲明一

        [DllImport("User32.dll")]  private static extern bool ShowWindowAsync(    IntPtr hWnd, int cmdShow);
        [DllImport("User32.dll")]  private static extern bool    SetForegroundWindow(IntPtr hWnd);
        private const int WS_SHOWNORMAL = 1;

        [STAThread]  public static void Main()
        {
            //得到正在啟動並執行常式
            Process instance = RunningInstance();
            if (instance == null)
            {
                //如果沒有其它常式，就建立一個表單
                Application.Run (new MainForm());
            }
            else
            {
                //處理髮現的常式
                HandleRunningInstance(instance);
            }
        }
        public static Process RunningInstance()
        {
            Process current = Process.GetCurrentProcess();
            Process[] processes = Process.GetProcessesByName (current.ProcessName);
            //遍曆正在有相同名字啟動並執行常式
            foreach (Process process in processes)
            {
                //忽略現有的常式
                if (process.Id != current.Id)
                {
                    //確保常式從EXE檔案運行
                    if (Assembly.GetExecutingAssembly().Location.Replace("/", "\\") ==current.MainModule.FileName)
                    {
                        //返回另一個常式執行個體
                        return process;
                    }
                }
            }
            //沒有其它的常式，返回Null
            return null;
        }
        public static void HandleRunningInstance(Process instance)
        {
            //確保視窗沒有被最小化或最大化
            ShowWindowAsync (instance.MainWindowHandle , WS_SHOWNORMAL);
            //設定真執行個體程為foreground window
            SetForegroundWindow (instance.MainWindowHandle);
        }
        
    }
}